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Re: How do you intend to maintain identical currents

Posted by ChasLieb (A) on March 23, 2007 at 12:54:51

In Reply to: Do you see a potential for oscillation? posted by Allen Wright on March 23, 2007 at 08:49:55:

I intend to use the 421A also designated the 5998. This is a dual triode in a single envelope. I intend to use each tube as its own PP pair. It is my hope that the two triodes in the tube will age at the same rate. I will use a dual triode driver stage, preferably direct coupled but possibly transformer coupled.

I will have to make periodic measurements on the cathodes to make sure bias voltage doesn't drift but I can see no way, short of using two separate current sources on the plates, to ensure that each tube draws the same current. Although this would seem a way to control both total current and the current of each stage, I have been warned off by others builders who told me I cannot have a current source both on the anode and cathode. I am not sure why this is. I have spoken to other builders who built self adjusting servo circuits but I am not that experienced a designer to craft one. As to the current source, I will have to use one capable of handling the probable 250 ma on the joined cathodes so I may use a a FET with a substantial heat sink. A smaller current source on the driver tube will suffice.

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